The present invention relates to the synthesis of large-sized diamonds. More specifically, the present invention relates to a method for joining diamond substrates to produce a large homoepitaxial monocrystalline diamond.
A natural diamond is a diamond that is formed naturally in the earth by the prolonged exposure of carbon-bearing materials to high pressure and temperature. Long periods of exposure to high pressures and temperatures make natural diamond crystals grow larger. Scientists have been able to produce synthetic diamonds in laboratory conditions, which have the same chemical composition and physical properties as natural diamonds. Synthetic diamonds are used in precision-cutting tools, heat sinks in electronics, telecommunications equipment, computers and integrated circuits, as anvils for pressure cells, and optical windows in laser equipment. Synthetic diamonds are also used in jewelry and ornaments. The price of a diamond is determined by the four ‘Cs’, i.e., cut, color, clarity and carat size. Other parameters being constant, the price of the diamond increases exponentially with its size.
Synthetic diamonds can be produced by a variety of methods. One such method uses high pressure high temperature (HPHT) to produce synthetic diamonds. A carbon substrate such as graphite is exposed to a pressure exceeding 50 kilobars and a temperature exceeding 1200° C. in the presence of a catalyst metal such as nickel, cobalt or iron, to grow a diamond. The diamond so produced is known as a HPHT grown diamond. However, it is generally difficult and expensive to produce a large-sized, high-quality monocrystalline diamond by the HPHT method. Another method, chemical vapor deposition (CVD), is used to synthesize diamonds from the gas phase at below atmospheric pressures and temperatures above 800° C. A mixture of hydrogen and a hydrocarbon gas is activated by a variety of methods, such as thermal (hot filament) or plasma (direct current, radio frequency or microwave) activation, or the use of a combustion flame (oxyacetylene or plasma torches). This dissociates the hydrogen gas into atomic hydrogen and the hydrocarbon gas into active carbon ions, atoms or CH radicals, which deposit on a substrate to form a diamond. The diamond so produced is known as a CVD grown diamond. A common disadvantage of existing CVD methods for the synthesis of diamonds is that the length and width of the CVD grown diamond is limited by the size of the substrate. Another limitation is the time taken by existing CVD methods to produce diamonds with a large volume and surface area. Existing CVD methods are time-consuming processes, since they take a large amount of time to produce diamonds with a large volume and surface area from a single substrate. Therefore, these methods are not very economical.
The applications of synthetic diamonds, particularly in electronics, suffer from the limitation that single diamond crystals with a large volume and surface area are not commercially available. Large single diamond crystals can be used in high pressure devices, large heat sinks for high power thermal management, large semiconductor devices, large infrared or high power microwave windows, electron field emission sources, and surface acoustic wave devices.
Hence, there exists a need for a method for producing a large homoepitaxial monocrystalline diamond with a large volume and surface area, in which the length and width of the diamond is not limited by the size of a substrate. Further, the method should be less time-consuming and more economical.